This from the EE website:
"Orange & T-Mobile today announced they will offer iPhone 5, the thinnest and lightest iPhone ever, to customers in UK beginning Friday, September 21. For more information please visit:
http://www.orange.co.uk/iphone5 or
http://www.t-mobile.co.uk/iphone5. For more information on iPhone 5, please visit:
http://www.apple.com/iphone.
Orange and T-Mobile iPhone 5 customers will also be able to move to EE to get superfast 4G when it launches in the coming weeks. They can register their interest at www.ee.co.uk."
Sounds like the EE won't be available at the iPhone launch but if you go with Orange or T-Mobile, they'll make it easy to switch to the 4G network.